Rotary transmitter for machine tools

ABSTRACT

The invention relates to a rotary transmitter ( 2 ) for machine tools, having an inductive energy transmission section ( 31 ), which is arranged between a stator part ( 4 ) fixed to the machine and a rotor part ( 6 ) fixed to the tool, and a contactless bidirectional data transmission section ( 35 ). A special feature of the invention consists in that, in order to make maximum use of the capacity of the energy transmission section ( 31 ), precautions are taken with which the optimal operating frequency (f opt ) of the energy transmission operating according to the transformer principle is determined at every system start in a test run with a connected test resister ( 51 ) and a variable frequency (f p ). Furthermore, for the purpose of interference-free data transmission, buffer storage of the data to be transmitted via the data transmission section ( 35 ) is proposed, which data are synchronised in predefined time windows with interference-free periods of the energy transmission.

The invention relates to a rotary transmitter for machine tools, havingan inductive transmission section for electrical power, having a statorpart, which is fixed to the machine, and a rotor part, which is fixed tothe tool and can rotate about a rotation axis, wherein the stator parthas a primary winding, which is arranged in a primary circuit, and therotor part has a secondary winding, which is arranged in a secondarycircuit and is separated from the primary winding by means of an airgap.

Rotary transmitters of this kind are used, for example, in machine toolshaving adjustment tools (EP 1 856 705 B1). In the known rotarytransmitters, a stator-end and a rotor-end power winding are in eachcase provided for inductive power transmission in accordance with thetransformer principle. The power windings are separated from one anotherby in each case a stator-end and a rotor-end core part, wherein thestator-end and rotor-end core parts face one another across an air gapat mutually facing ends. In addition, stator- and rotor-end transmissionand reception elements are provided in the known rotary transmitter,said stator- and rotor-end transmission and reception elements havingstator- and rotor-end coupling turns, which are associated with oneanother in pairs, for inductive data transmission and being connected toa transmission and reception electronics system. An essentialrequirement of these rotary transmitters is that high electrical powersand large quantities of data can be transmitted given the lowestpossible installation space. In addition, the systems should be robustand easy to handle since they have to operate in a reliable manner underharsh environmental and use conditions. Both in respect of productionusing components which are subject to tolerances and the partialmechanical manufacture of the coupling elements and also in respect ofpractical use, in which rotor, stator and actuation electronics systemshave to be able to be replaced in the event of repair and maintenance,there are differences in the components, it being possible for thesedifferences to influence both power and data transmission. In addition,owing to the physical proximity of power and data transmission elements,the compact design on offer exhibits the problem that power transmissioncan interfere with data transmission. Despite various structuralmeasures for reducing this influence by means of shielding,symmetrization and interference-reduced circuit technology, this meansthat the transmission power, the reduction in installation space, thedata rate, the flexibility and not least the system costs are subject tolimits which restrict the field of application.

Proceeding from this, the invention is based on the object of increasingthe power which can be transmitted on the power transmission section,without interfering with data transmission in the process.

The combinations of features indicated in patent claims 1, 2, 7, 9 and10 are proposed for achieving this object. Advantageous refinements anddevelopments of the invention can be found in the dependent claims.

The solution according to the invention is based on the knowledge thatin order to transmit the electrical power from the stationary stator tothe rotating rotor in accordance with the transformer principle saidpower has to be in the form of an alternating current or AC voltage.Since mains power is not suitable for direct transmission owing to theexcessively low frequency (50 Hz) and the excessively high voltage (230volts), a suitable alternating current has to be produced in the rotarytransmitter itself. To this end, a power supply unit is used to providea DC voltage which is converted by means of an inverter into an ACvoltage with a suitable frequency. On the secondary side, the AC voltageis converted back into a DC voltage by means of a rectifier and a buffercapacitor. In addition, the contact-free transmission of power across anair gap in accordance with the transformer principle has thedisadvantage that the degree of coupling between the primary winding andthe secondary winding is considerably less than 1 and changes as thesize of the air gap changes. In addition, the inductances of the primaryand the secondary winding change as the air gap changes. In order toachieve optimum power output, the coupler has to be operated at aspecific frequency close to the natural frequency of the secondaryresonant circuit. Since said natural frequency changes as the size ofthe air gap changes and on account of the various component tolerances,the process cannot be based on a constant natural frequency. Theinvention therefore makes provision for the frequency to be newlydetermined and prespecified each time the system is started, with theresult that the system can always be operated at an optimum operatingfrequency on the power transmission section even under changedconditions, such as a change in the tool head, a deviation in the airgap or an exchange of assemblies.

In order to achieve this, the invention proposes a procedure whichcomprises the following method steps each time the system is started:

-   -   in a first step a test resistor is connected into the secondary        circuit,    -   in a second step a measure for the electrical load power in the        primary circuit or in the secondary circuit is ascertained as a        function of the alternating current frequency in the primary        circuit,    -   in a third step an optimum alternating current frequency in the        primary circuit, at which frequency the electrical load power is        at a maximum, is ascertained,    -   in a fourth step an operating frequency of the alternating        current for transmitting electrical power from the stator part        to the rotor part is set in the primary circuit, the value of        said operating frequency corresponding to the optimum        alternating current frequency.

In respect of circuitry, the above object can be achieved

-   a) in that an inverter is arranged in the primary circuit, the DC    input of said inverter being connected to a DC source, the AC output    of said inverter being connected to a primary resonant circuit which    contains the primary winding, and it being possible to vary and    adjust the operating frequency of said inverter by means of a    control assembly;-   b) in that a rectifier is arranged in the secondary circuit, a    secondary resonant circuit which contains the secondary winding    being connected to the AC input of said rectifier, and the DC output    of said rectifier being in the form of a load connection, wherein    the secondary circuit comprises a test resistor which can be    selectively connected and bridges the load connection.-   c) In a first variant embodiment of the invention, an ammeter also    is arranged in the primary circuit at the DC input of the inverter,    while the control assembly has a programmable actuating output,    which is connected to a frequency input of the inverter, and a    measurement input which is connected to or communicates with the    ammeter.-   c′) In a second variant embodiment of the invention, a voltmeter,    which records the voltage drop across the test resistor, is arranged    in the secondary circuit, while the control assembly has a    programmable actuating output, which is connected to a frequency    input of the inverter, and also a measurement input which    communicates wirelessly with the voltmeter.

In order to arrive at the desired objective, according to a preferredrefinement of the invention, the control assembly has an evaluationcircuit or routine for storing and/or evaluating the measurement values,which are received by means of the measurement input in the form ofmeasurement signals, as a function of the frequency values, which areoutput by means of the actuating output in the form of frequencysignals, when the test resistor is connected, and also has a data memoryfor storing an optimum operating frequency which is calculated using theevaluation circuit or routine. In other words, this means that thecontrol assembly sets the frequency of the alternating current, which isoutput by the inverter, to an optimum operating frequency which is closeto the resonant frequency of the secondary resonant circuit.

A further preferred refinement of the invention makes provision for arespective transmission and reception element for contact-freebidirectional data transmission to be arranged in the stator part and inthe rotor part. When the AC voltage for power transmission is inherentlyproduced in an inverter in the manner of a square-wave voltage,relatively high-frequency interference signals, which can lead tointerference in data transmission owing to the compact arrangement ofpower and data transmission sections in the rotary transmitter, occurprimarily at the zero crossings. In order to avoid this, it is alsoproposed according to the invention

a) that the data is transmitted by means of the bidirectional datatransmission section in the form of data packets in time windows,

b) that the information relating to the temporal position of the zerocrossing of an alternating current in the power transmission section isascertained,

c) and that, on the basis of the information relating to the temporalposition of the zero crossing of the alternating current in the primarycircuit or in the secondary circuit of the power transmission section,the time windows for the transmission of the data packets areestablished such

-   -   that the time windows lie between two successive zero crossings        of the alternating current    -   and each have a start and an end point which are at a time        interval from the zero crossings of the alternating current.

In respect of circuitry, this can be realized according to the inventionin that the stator-end and the rotor-end transmission element areconnected to a respective control assembly which contains a buffermemory in which data packets for transfer to the associated rotor-end orstator-end reception element in a defined time window are stored,wherein the length of the time window is smaller than half the period ofthe alternating current which flows through the primary winding in theprimary circuit and/or the secondary winding in the secondary circuit,and wherein the start and the end of the time window are at a timeinterval from the successive zero crossings of the alternating currentwhich flows through the primary winding and/or the secondary winding.

The invention will be explained in greater detail below with referenceto the exemplary embodiments which are schematically illustrated in thedrawing, in which

FIG. 1 shows a partially sectioned illustration of a side view of a toolhead, which is clamped into a machine spindle, with a rotary transmitterfor power and data transmission;

FIG. 2 shows a circuit diagram of the rotary transmitter with astator-end primary circuit and a rotor-end secondary circuit; and

FIG. 3 shows an optimization diagram for determining the optimumoperating frequency of the power transmission section.

The rotary transmitter illustrated in FIG. 2 is intended to be used inthe region of a replaceable tool head of a machine tool, as illustratedby way of example in FIG. 1. The tool head 60, which is shown in FIG. 1and is in the form of a precision turning head, substantially comprisesa main body 68, a slide 70 which can be adjusted transversely in thedirection of the arrow 74 in relation to the rotation axis 64 of thetool head 60 and has a cutting tool 72, at least one electrical load 50which is arranged within the tool head 60, for example in the form of ameasuring device 78 for direct adjustment movement measurement, and anelectric adjusting motor 76 for the slide 70. Power is supplied for theelectrical load 50 and the data interchange by means of the rotarytransmitter 2 which comprises a stator part 4 and a rotor part 6. Thetool head 60 can be coupled to the machine spindle 62 of a machine tool63 by way of a tool shank 80 which projects axially beyond the mainbody. In order to set an air gap 37 between the stator part 4 and therotor part 6, the stator housing 82 is arranged on a holder 86, which isfixed to the stator, by means of an adjustment mechanism 88 such thatboth its distance from the rotor and its rotary position about an axiswhich is parallel in relation to the rotation axis 64 can be adjusted.In the exemplary embodiment shown in FIG. 1, the stator part 4 extendsin the manner of a segment only over a portion of the circumference ofapproximately 60° to 100° of the tool shank 80 and leaves the majorityof the shank circumference free, so as to form a free space 90 foraccess by a tool gripper 92 for automatic tool changing. When the toolis changed, the tool head 60 is grasped at the gripper groove 96 by thetool gripper 92 from that side which is opposite the stator part 4, andis moved axially with respect to the machine spindle 62 when the toolcoupling is released. The tool head 60 is coupled to the machine spindle62 by means of a clamping mechanism which can be operated on the machineside by means of a tie rod 98, engages from the machine side into thehollow space 100 in the tool shank 80, and couples the tool head 60 tothe machine spindle 62 so as to produce planar surface clamping andradial clamping.

As shown in FIG. 2, the rotary transmitter 2 has an inductive powertransmission section 31 which comprises the stator part 4, which isfixed to the machine and has already been described in connection withFIG. 1, and the rotor part 6, which is fixed to the tool and can rotateabout a rotation axis 64. The stator part 4 has a primary winding 10,which is arranged in a primary circuit 8, and the rotor part 6 has asecondary winding 38, which is arranged in a secondary circuit 36 and isseparated from the primary winding 10 by means of the air gap 37.

An inverter 12 is arranged in the primary circuit 8, the DC input 14, 16of said inverter being connected to a DC source 7, 9, and the AC output18, 20 of said inverter being connected to a primary resonant circuitwhich contains the primary winding 10. The operating frequency of theinverter 12 can be set by means of a stator-end control assembly 24. Arectifier 40 is located in the rotor-end secondary circuit 36, asecondary resonant circuit which contains the secondary winding 38 beingconnected to the AC input 42, 44 of said rectifier, and the DC output46, 48 of said rectifier being in the form of a connection for therotor-end electrical load 50.

A data transmission section 35 is also located between the stator part 4and the rotor part 6, said stator part and rotor part having arespective transmission and reception element 106, 108 and,respectively, 106′, 108′ for contact-free bidirectional datatransmission, said transmission and reception elements each having atransmission and reception electronics system 110, 112 and, respectively110′, 112′. The transmission and reception elements are actuated bymeans of the stator-end control assembly 24 or the rotor-end controlassembly 56. The transmission and reception elements are expedientlyconstituent parts of an inductive, capacitive or optical datatransmission section.

Contact-free power transmission across the air gap 37 in accordance withthe transformer principle has the advantage that the degree of couplingbetween the stator-end primary winding 10 and the rotor-end secondarywinding 38 is considerably less than 1 and changes as the size of theair gap 37 changes. In addition, the inductances of the primary and thesecondary winding 10, 38 change as the size of the air gap 37 changes.In order to achieve optimum power transmission, the primary circuit 8and the secondary circuit 36 have to be operated at an optimum frequencywhich corresponds approximately to the natural frequency of thesecondary circuit. Since the natural frequency changes as the size ofthe air gap changes and the tolerances of various components in thestator and rotor part 4, 6 change, the operating frequency has to beadjusted each time the system is started.

To this end, the secondary circuit 36 has a test resistor which can beselectively connected by means of the switch 53 and bridges the DCoutput 46, 48 in the region of the load connection. In addition,according to a first variant embodiment, an ammeter 28 is arranged inthe primary circuit at the DC input 14, 16 of the inverter 12, theoutput 30 of said ammeter communicating with a measurement input 32 ofthe stator-end control assembly 24. As an alternative to this, accordingto a second variant embodiment, a voltmeter 102, which records thevoltage drop across the test resistor 51, is arranged in the secondarycircuit, the output of said voltmeter communicating with a measurementinput 39 of the stator-end control assembly 24, for example, by means ofa data transmission section 41.

In both variant embodiments, the stator-end control assembly 24 has aprogrammable actuating output 26 which is connected to the frequencyinput 22 of the inverter 12. For its part, the control assembly 24 hasan evaluation circuit or routine for storing and/or evaluating themeasurement values from the ammeter 28 or from the voltmeter 102, whichmeasurement values are received by means of the measurement input 32and, respectively, 39 in the form of measurement signals, as a functionof the frequency values f_(p), which are output by means of theactuating output 26 in the form of frequency signals S, when the testresistor 51 is connected, and also has a data memory for storing anoptimum operating frequency f_(opt) which is calculated by way of theevaluation circuit or routine. This circuit arrangement operates asfollows:

once the rotary transmitter 2 is activated, the stator-end controlassembly 24 prespecifies a fixed alternating frequency, which is roughlyin the range of the later operating frequency, to the inverter 12 for ashort time. In the process, power is transmitted from the stator end tothe rotor end, it being possible for the rotor-end control assembly 56to begin to operate using said power. Said control assembly firstconnects the test resistor 51 by means of the output 59 and the switch53, said test resistor receiving the transmitted power by means of theDC output 46, 48 of the rectifier 40 and therefore providing thesecondary resonant circuit with a low impedance for the naturalfrequency, that is to say providing it with a certain quality.

Subsequently, the stator-end control assembly 24 begins to run through aprespecified frequency range in steps. In the process, at each frequencystep, either the current consumption I of the inverter 12 is measured bymeans of the ammeter 28 or the voltage drop U across the test resistor51 is measured by means of the voltmeter 102 and stored with theassociated frequency values f_(p) so as to form a curve 140 (FIG. 3). Ifthe natural frequency of the rotor-end secondary resonant circuit is nowwithin the frequency range which has been run through, it is possible toestablish either a current maximum 142 or a voltage maximum 144 in thatrange (cf. FIG. 3).

The evaluation circuit or routine which is present in the stator-endcontrol assembly 24 now determines the frequency belonging to thecurrent maximum 142 or voltage maximum 144, possibly further adjustssaid frequency with a correction value and stores it as the optimumoperating frequency f_(opt) in a data memory for the subsequentactuation of the inverter 12. The test resistor 51 is then disconnectedby means of the switch 53, with the result that the total power whichcan be transmitted is now available to the electrical load 50.

As already explained above, both an inductive power transmission section31 and a contact-free bidirectional data transmission section 35 areprovided between the stator part 4 and the rotor part 6 of the rotarytransmitter 2. The AC voltage for the power transmission is inherentlyproduced in the inverter 12, which is connected to a DC source, in themanner of a square-wave voltage. When the DC voltage is chopped into theAC voltage, relatively high-frequency interference occurs primarily atthe zero crossings, but this interference quickly dissipates. At a timeinterval from each zero crossing, there is a relatively long time perioduntil the next zero crossing in which there is no interference.Secondly, the data does not have to be continuously transmitted by meansof the data transmission section 35 when there is a sufficiently highbit rate. According to the invention, this can be used for the purposeof transmitting the data in time windows with interposed transmissionbreaks by means of the bidirectional data transmission section 35 in theform of data packets 180, 182, 176, 178. In order to ensureinterference-free transmission, the information relating to the temporalposition of the zero crossing of the alternating current in the powertransmission section is first ascertained. On the basis of theinformation relating to the temporal position of the zero crossing ofthe alternating current of the power transmission section, the timewindows for the transmission of the data packets 180, 182, 176, 178 areestablished such that they are between two successive zero crossings ofthe alternating current, and that they each have a start and an endpoint which are at a time interval from the zero crossings of thealternating current.

In respect of circuitry, this is realized according to FIG. 2 in thatthe stator-end and the rotor-end transmission element are connected to arespective control assembly 24, 56 which contains a respective buffermemory 34, 58 in which data packets 180, 182 and, respectively, 176, 178for transmission by means of the associated rotor-end or stator-endtransmission elements 106, 106′ in a defined time window are stored. Inthis case, the data packets 180, 182, 176, 178 are dimensioned such thatthe length of the associated time window is smaller than half the periodof the alternating current which flows through the primary winding 10 inthe primary circuit 8 and/or the secondary winding 38 in the secondarycircuit 36, and wherein the start and the end of the time window are ata time interval from the successive zero crossings of the alternatingcurrent which flows through the primary winding 10 and/or the secondarywinding 38. Data transmission which is not adversely affected bychangeover interference in the power transmission section is achieved byway of this measure, despite the compact design of the rotarytransmitter 2.

In summary, the following can be stated: the invention relates to arotary transmitter 2 for machine tools, having an inductive powertransmission section 31, which is arranged between a stator part 4,which is fixed to the machine, and a rotor part 6, which is fixed to thetool, and also having a contact-free bidirectional data transmissionsection 35. A special feature of the invention is that precautions aretaken for the purpose of utilizing the capacity of the powertransmission section 31 to the maximum extent, whereby the optimumoperating frequency f_(opt) of the power transmission process, whichoperates in accordance with the transformer principle, is ascertained ina test run with the test resistor 51 connected and at the variablefrequency f_(p) each time the system is started. Furthermore, for thepurpose of interference-free data transmission, it is proposed that thedata which is to be transmitted by means of the data transmissionsection 35 is temporarily stored, this temporary storage beingsynchronized in prespecified time windows with interference-free timeperiods of power transmission.

List of Reference Symbols

-   2 Rotary transmitter-   4 Stator part-   6 Rotor part-   7, 9 DC source-   8 Primary circuit-   10 Primary winding-   12 Inverter-   14 Slide-   14, 16 DC input-   18, 20 AC output-   22 Frequency input-   24 Stator-end control assembly-   26 Actuating output-   28 Ammeter-   30 Output-   31 Power transmission section-   32 Measurement input (I)-   34 Buffer memory, data memory-   35 Data transmission section-   36 Secondary circuit-   37 Air gap-   38 Secondary winding-   39 Measurement input (U)-   40 Rectifier-   41 Data transmission section-   42, 44 AC input-   46, 48 DC output-   50 Electrical load-   51 Test resistor-   53 Switch-   56 Rotor-end control assembly-   58 Buffer memory-   59 Output-   60 Tool head-   62 Machine spindle-   63 Machine tool-   64 Rotation axis, rotary axis-   68 Main body-   70 Slide-   72 Cutting tool-   74 Arrow-   76 Electrical adjusting motor-   78 Measuring device-   80 Tool shank-   82 Stator housing-   86 Holder which is fixed to the stator-   88 Adjustment mechanism-   90 Clearance-   92 Tool gripper-   96 Gripper groove-   98 Tie rod-   100 Hollow space-   102 Voltmeter-   106, 108 Transmission and reception element (stator-end)-   106′, 108′ Transmission and reception element (rotor-end)-   110, 112 Transmission and reception electronics (stator-end)-   110′, 112′ Transmission and reception electronics (rotor-end)-   140 Curve-   142 Current maximum-   144 Voltage maximum-   176, 178, 180, 182 Data packet-   I Current-   U Voltage-   f_(p) Frequency-   f_(opt) Optimum operating frequency

1. A rotary transmitter (2) for machine tools, having an inductivetransmission section (31) for electrical power, having a stator part(4), which is fixed to the machine, and a rotor part (6), which is fixedto the tool and can rotate about a rotation axis (64), wherein thestator part (4) has a primary winding (10), which is arranged in aprimary circuit (8), and the rotor part has a secondary winding (38),which is arranged in a secondary circuit (36) and is separated from theprimary winding by means of an air gap, characterized in that aninverter (12) is arranged in the primary circuit (8), the DC input (14,16) of said inverter being connected to a DC source (7, 9), the ACoutput (18, 20) of said inverter being connected to a primary resonantcircuit which contains the primary winding (10), and it being possibleto vary and adjust the operating frequency of said inverter by means ofa control assembly (24), in that a rectifier (40) is arranged in thesecondary circuit (36), a secondary resonant circuit which contains thesecondary winding (38) being connected to the AC input (42, 44) of saidrectifier, and the DC output (46, 48) of said rectifier being in theform of a load connection, in that the secondary circuit comprises atest resistor (51) which can be selectively connected and bridges theload connection, in that an ammeter (28) is arranged in the primarycircuit at the DC input (14, 16) of the inverter (12), and in that thecontrol assembly (24) has a programmable actuating output (26), which isconnected to the frequency input (22) of the inverter (12), and ameasurement input (32) which is connected to or communicates with theammeter (28).
 2. The rotary transmitter (2) for machine tools, having aninductive transmission section (31) for electrical power, having astator part (4), which is fixed to the machine, and a rotor part (6),which is fixed to the tool and can rotate about a rotation axis (64),wherein the stator part (4) has a primary winding (10), which isarranged in a primary circuit (8), and the rotor part (6) has asecondary winding (38), which is arranged in a secondary circuit (36)and is separated from the primary winding (10) by means of an air gap(37), characterized in that an inverter (12) is arranged in the primarycircuit (8), the DC input (14, 16) of said inverter being connected to aDC source (7, 9), the AC output (18, 20) of said inverter beingconnected to a primary resonant circuit which contains the primarywinding (10), and it being possible to vary and adjust the operatingfrequency of said inverter by means of a control assembly (24), in thata rectifier (40) is arranged in the secondary circuit (36), a secondaryresonant circuit which contains the secondary winding (38) beingconnected to the AC input (42, 44) of said rectifier, and the DC output(46, 48) of said rectifier being in the form of a load connection, inthat the secondary circuit comprises a test resistor (51) which can beselectively connected and bridges the load connection, in that avoltmeter (102), which records the voltage drop across the test resistor(51), is arranged in the secondary circuit, and in that the controlassembly (24) has a programmable actuating output (26), which isconnected to the frequency input (22) of the inverter (12), and also ameasurement input (39) which communicates wirelessly with the voltmeter(102).
 3. The rotary transmitter as claimed in claim 1, characterized inthat the control assembly (24) has an evaluation circuit or routine forstoring and/or evaluating the measurement values, which are received bymeans of the measurement input (32) in the form of measurement signals,as a function of the frequency values, which are output by means of theactuating output (26) in the form of frequency signals, when the testresistor (51) is connected, and also has a data memory for storing anoptimum operating frequency which is calculated using the evaluationcircuit or routine.
 4. The rotary transmitter as claimed in claim 1,characterized in that the control assembly (24) sets the frequency ofthe alternating current, which is output by the inverter (12), to anoperating frequency which is close to the resonant frequency of thesecondary resonant circuit.
 5. The rotary transmitter as claimed inclaim 1, characterized in that a respective transmission and receptionelement (106, 108, 106′, 108′) for contact-free bidirectional datatransmission is arranged in the stator part (4) and in the rotor part(6).
 6. The rotary transmitter as claimed in claim 5, characterized inthat the stator-end and the rotor-end transmission element (106, 106′)are connected to a respective control assembly (24, 56) which contains abuffer memory (34, 58) in which data packets (180, 182; 176, 178) fortransfer to the associated rotor-end or stator-end reception element(108, 108′) in a defined time window are stored, wherein the length ofthe time window is smaller than half the period of the alternatingcurrent which flows through the primary winding (10) and/or thesecondary winding (38), and wherein the start and the end of the timewindow are at a time interval from the successive zero crossings of thealternating current which flows through the primary winding (10) and/orthe secondary winding (38).
 7. A rotary transmitter for machine tools,having an inductive transmission section for electrical power, having astator part (4), which is fixed to the machine and has a primary winding(10) which is arranged in a primary circuit (8), having a rotor part(6), which is fixed to the tool and can rotate about a rotation axis(64) and has a secondary circuit (36) with a secondary winding (38)which are separated from the primary winding (10) by means of an air gap(37), and having stator- and rotor-end transmission and receptionelements (106, 108, 106′, 108′) for bidirectional contact-free datatransmission, characterized in that the stator-end and the rotor-endtransmission element (106, 106′) are connected to a respective controlassembly (24) which contains a buffer memory (34, 58) in which datapackets (108, 182, 176, 178) for transfer to the associated rotor-end orstator-end reception element (108, 108′) in a defined time window arestored, wherein the length of the time window is smaller than half theperiod of the alternating current which flows through the primarywinding (10) and/or the secondary winding (38), and wherein the startand the end of the time window are at a time interval from thesuccessive zero crossings of the alternating current which flows throughthe primary winding (10) and/or the secondary winding (38).
 8. A toolhead having an electrical load (50) and having a rotary transmitter (2)which is designed as claimed in claim 1, characterized in that theelectrical load (50) is in the form of an electric motor (76), which canbe connected to the secondary circuit (36), for adjusting a slide (70)and/or in the form of an actuator for cutting adjustment and/or in theform of a laser and/or in the form of an inductor and/or in the form ofan electrically actuable spray unit for a quenching fluid and/or in theform of an apparatus for welding, soldering, heating, curing, coating orlabeling a workpiece.
 9. A method for the inductive transmission ofelectrical power by means of a rotary transmitter (2) from a stator part(4), which is fixed to the machine and has a primary circuit (8), to arotor part (6), which is fixed to the tool and has a secondary circuit(36), over a power transmission section (31) in a machine tool,characterized in that in a first step a test resistor (51) is connectedinto the secondary circuit (36), in that in a second step a measure forthe electrical load power in the primary circuit (8) or in the secondarycircuit (36) is ascertained as a function of the frequency (f_(p)) of analternating current in the primary circuit (8), in that in a third stepan optimum frequency (f_(opt)) of the alternating current in the primarycircuit (8), at which frequency the electrical load power is at amaximum, is ascertained, and in that in a fourth step an operatingfrequency of the alternating current in the primary circuit (8) fortransmitting electrical power from the stator part (4) to the rotor part(6) is set, the value of said operating frequency corresponding to theoptimum frequency (f_(opt)).
 10. A method for transmitting data over adata transmission section (35) by means of a contact-free rotarytransmitter (2) which also has an inductive power transmission section(31), in which method the data is transmitted in the form of datapackets (180, 182, 176, 178) in time windows, characterized in that theinformation relating to the temporal position of the zero crossing of analternating current in the power transmission section (31) isascertained, and in that, on the basis of the information relating tothe temporal position of the zero crossing of the alternating current ina primary circuit (8) or in a secondary circuit (36) of the powertransmission section, the time windows for the transmission of the datapackets (180, 182, 176, 178) is established such that the time windowslie between two successive zero crossings of the alternating current andeach have a start and an end point which are at a time interval from thezero crossings of the alternating current.